I could spend hours with these maps: for example, it’s amazing to see that agricultural activity in India in 1700 is as intensive, if not more so, than in the traditional bread-baskets of the Caucasus or the densely populated areas of Northern Europe. The persistent un-farmed patch of France’s Massif Central is also interesting: even the Alps appear to have more agricultural activity.

Rankin notes that the major trend of the past three hundred years is simply the intensification of farming practices on land that was already agricultural, “punctuated by several episodes of rapid expansion into previously untapped areas: the Great Plains in the late nineteenth century, Argentina in the early twentieth century, and in last few decades, Brazil and central India.” He also points out rare but occasional declines in agricultural density: in the “central Amazon, northern Patagonia, or the Appalachian Piedmont after World War II.”

You might be wondering how Rankin knows what percentage of land was used for growing crops in 1700, before much of the world had even been charted, let alone systematically analysed in terms of land-use.

The dataset on which Rankin’s animation is based was developed by Navin Ramankutty and Jonathan Foley, whose methodology relied on an assessment of global agricultural land in 1992, at “5 min spatial resolution” (about 10 km at the equator), by “calibrating a remotely sensed land cover classification data set against cropland inventory data.” They then compiled an “extensive database of historical cropland inventory data, at the national and subnational level, from a variety of sources,” and processed that information through their 1992 land cover/inventory algorithm, in order to arrive at a historical reconstruction.

As Ramankutty and Foley freely acknowledge, the resulting map is a guess, albeit an extremely educated one that also matches what we know of “the history of human settlement and patterns of economic development.”

As always, much of the interest in maps like these lies in thinking about what is or isn’t measured—and why. Personally, I’m intrigued by the intensification metric, and the visual implication, as Bill Rankin puts it, that “many agricultural areas are at close to 100% exploitation.” This doesn’t seem quite right: Ramankutty and Foley are measuring agricultural land use (and only at a resolution of about 10 km at the equator), not productive potential. After all, surely an area of land could be solely devoted to agriculture and yet produce wildly differing yields depending on the crops sown and the farming techniques used?

IMAGE: Map showing the suitability of land for agriculture. The map (larger view here) is derived from more data sets developed by Ramankutty and Foley, available at the Atlas of the Biosphere.

Elsewhere, Ramankutty and Foley have also collaborated to map agricultural potential, based on “the temperature and soil conditions of each grid cell.” Somewhat implausibly, since agriculture both shapes and is shaped by human civilisation, the suitability rating ignores human inputs—urban sprawl, artificial irrigation, topsoil creation—altogether.

Stepping even further away from plausibility (and human intervention), Ramankutty and Foley subsequently produced a fascinating map of potential vegetation, showing “the vegetation that would exist at a given location had human forms of land use never existed.”

It is an alternate surface of the earth, carefully surveyed and classified by a human civilization that could not have existed in order for it to be a reality.

On a similar note, Colorado State University researcher David Theobald has designed a new system for evaluating and mapping the “naturalness” of a landscape. In his review, Rob Goldstein describes Theobald’s methodology thus:

Specifically, Theobald used existing land use data to apply scores at a scale of 30 metres. Urban/built-up areas, roads and cropland were assigned a score of “0.” Natural areas (i.e. forests, grassland, wetlands, etc.) were assigned a score of “1.” Roads and rural development negatively impacted the scores of adjacent areas.

Using this technique, Theobald arrived at “a natural landscape score of .6621 for the conterminous United States in 2001.” In other words, the lower forty-eight states are sixty-six percent “natural,” and only one-third human-designed, or “unnatural.”

The project seems flawed on several levels (it is somewhat incredible that Owens Valley, with its hijacked river and poisonous lake-bed, could receive the “highest naturalness” scores under any rubric), but the paradox of its premise is fascinating—that a pure form of nature can be carefully located and recognised as such by humans whose activity otherwise renders impossible its very existence.

Theobald suggests that his system is a useful tool for conservationists seeking to prioritise their efforts. To me, however, it is more interesting as a geographic expression of impossible nostalgia—the land-use database equivalent of medieval monks calculating how many angels could dance on a pin.

3 Comments

1. Regarding the “Agricultural Suitability” map: I wonder if this map also shows the paths for human migration out of Africa. Suitability would mean good soil, which might also mean valley passages where soil would naturally accumulate.

2. I also wonder if the authors have made a map of agricultural suitability based only on climate – sunshine, temperature, rainfall, etc…. with the expectation that soil can be created and ported, e.g. from compost. In fact, in Wisconsin, we are having pollution problems caused by excess organic material (cow manure) washing into our lakes.

I’ll admit that I haven’t gone to the trouble of tracking down a copy of Theobald’s original paper, but it sounds from your description, the abstract, and Goldstein’s review as if it is quite simplistic in its methodology. As you note, if Owens Valley rates high in “naturalness”, then “naturalness” must mean not much more than “the absence of current human settlement”, which of course ignores the many ways in which humans affect places that they are not settled in — from occupation in the distant past to, as in the case of Owens Valley, the extraction of resources for distant settlements. (I’ve seen these sorts of landscapes referred to as “novel ecosystems” — “fragmented forests filled with species from other continents, forest plantations, abandoned grazing lands and so on”.)

Two comments on the naturalness index. One, so-called natural areas in the USA were inhabited by Native Americans. Two, there is nature in our cities, suburbs, and exurbs. Surprising that this type of analysis was developed recently.